In addition, black and Hispanic infants are more likely than white newborns to receive care at poor-quality NICUs, the study found.

While these trends are real, they were not present across the board, the researchers added. Some California hospitals provided better care to minority babies than white infants, for example.

The disparities in care are caused by many social, economic and organizational factors in the hospital and its surrounding community, said lead researcher Dr. Jochen Profit. He's an associate professor of pediatrics with the Stanford University School of Medicine.

Profit does not believe racism is one of those factors.

"I don't think any health care provider in the NICU or anywhere else goes to work and says, 'I'm going to provide worse care to African-American babies than white babies,'" Profit said. "Their goal is to provide the best care to all patients they see."

But these results show that some hospitals have not adapted to their specific patient populations well enough to adequately meet the needs of the community, Profit added.

"There's opportunity for improvement," Profit said.

For the study, Profit and his team reviewed data on premature births in California. They included more than 18,600 babies born with very low birth weight -- less than 3.3 pounds -- between 2010 and 2014.

The research team evaluated the NICU care each newborn received based on a set of nine yes/no questions. These included whether anyone died as a result of the birth, whether the baby suffered health problems such as infections or chronic lung disease, how quickly the newborn grew in the NICU, and whether the baby received a timely eye exam.

Although racial and ethnic differences in NICU care were fairly small across California as a whole, some hospitals had large gaps in how they care for babies of different backgrounds, researchers found.

Some of those disparities could result from the community in which the hospital is located, said Dr. Deborah Campbell, chief of neonatology at Children's Hospital at Montefiore in New York City.

"Hospitals with higher percentages of uninsured or Medicaid-insured patients may have fewer resources available to them," said Campbell, who wasn't involved in the study. "It's not necessarily intentional."

For example, medical teams in poorer communities may not be able to afford specialists that could improve care, such as respiratory therapists or nutritionists, Campbell said.

While that may be one factor, Profit does not believe it explains all the disparities found by his research team.

"There are some hospitals like that that actually do really well, even though their population would predict them to be one of our more lower-performing centers," Profit said. "The main message from this paper is it's not that simple."

Instead, Profit believes every hospital needs to individualize care.

One question used as a quality measure was whether newborns had received any mother's milk by the time they left the hospital, he noted.

"It requires a lot of team and parental engagement to support a mother who spends months of time after this traumatic birth in the NICU, and help her pump breast milk throughout that entire time," Profit said. "It's an arduous process, and requires a lot of education and support."

Traditionally, black mothers breast-feed at a lower rate than other ethnic subgroups, and likely require more counseling and assistance, he said.

"As expected, we find that babies of African-American moms receive less human milk by hospital discharge than their white counterparts," Profit said.

Another quality question involved whether moms were provided steroids prior to delivery, to better mature the lungs of their infants and provide them with other health benefits.

Researchers found that Hispanic women received these steroids less often than white women, Profit said.

That could be chalked up to insufficient communication and coordination between the expecting mother and her doctors, especially if she doesn't speak English, he said. Hispanic mothers simply may not have grasped that they needed to get to the hospital sooner so they could receive the steroids.

"Even though you may have language services available, parents may not receive the same level of information flow that they would get if communication was easier," Profit said.

Closing these gaps in care will require a lot of effort from hospitals and doctors, Profit said.

"A lot of the solutions to addressing these disparities in care require extra work by providers beyond the busy care for the baby's illness and keeping the baby stable and thriving and growing," he said. "You must go out of your way and address the needs of the vulnerable families."